better demonstrate usbnet exmaple is multiple configurations

examples/device/net_lwip_webserver/src/usb_descriptors.c

@@ -69,7 +69,7 @@ tusb_desc_device_t const desc_device =
     .iProduct           = STRID_PRODUCT,
     .iSerialNumber      = STRID_SERIAL,
 
-    .bNumConfigurations = 0x02
+    .bNumConfigurations = 0x02 // multiple configurations
 };
 
 // Invoked when received GET DEVICE DESCRIPTOR
@@ -91,8 +91,8 @@ enum
 
 enum
 {
-  CONFIG_NUM_DEFAULT = 1,
-  CONFIG_NUM_ALTERNATE = 2,
+  CONFIG_NUM_RNDIS = 1,
+  CONFIG_NUM_ECM   = 2,
 };
 
 #define MAIN_CONFIG_TOTAL_LEN    (TUD_CONFIG_DESC_LEN + TUD_RNDIS_DESC_LEN)
@@ -106,30 +106,41 @@ enum
   #define EPNUM_CDC     2
 #endif
 
-static uint8_t const main_configuration[] =
+static uint8_t const rndis_configuration[] =
 {
   // Config number, interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(CONFIG_NUM_DEFAULT, ITF_NUM_TOTAL, 0, MAIN_CONFIG_TOTAL_LEN, 0, 100),
+  TUD_CONFIG_DESCRIPTOR(CONFIG_NUM_RNDIS, ITF_NUM_TOTAL, 0, MAIN_CONFIG_TOTAL_LEN, 0, 100),
 
   // Interface number, string index, EP notification address and size, EP data address (out, in) and size.
   TUD_RNDIS_DESCRIPTOR(ITF_NUM_CDC, STRID_INTERFACE, 0x81, 8, EPNUM_CDC, 0x80 | EPNUM_CDC, CFG_TUD_NET_ENDPOINT_SIZE),
 };
 
-static uint8_t const alt_configuration[] =
+static uint8_t const ecm_configuration[] =
 {
   // Config number, interface count, string index, total length, attribute, power in mA
-  TUD_CONFIG_DESCRIPTOR(CONFIG_NUM_ALTERNATE, ITF_NUM_TOTAL, 0, ALT_CONFIG_TOTAL_LEN, 0, 100),
+  TUD_CONFIG_DESCRIPTOR(CONFIG_NUM_ECM, ITF_NUM_TOTAL, 0, ALT_CONFIG_TOTAL_LEN, 0, 100),
 
   // Interface number, description string index, MAC address string index, EP notification address and size, EP data address (out, in), and size, max segment size.
   TUD_CDC_ECM_DESCRIPTOR(ITF_NUM_CDC, STRID_INTERFACE, STRID_MAC, 0x81, 64, EPNUM_CDC, 0x80 | EPNUM_CDC, CFG_TUD_NET_ENDPOINT_SIZE, CFG_TUD_NET_MTU),
 };
 
+// Configuration array: RNDIS and CDC-ECM
+// - Windows only works with RNDIS
+// - MacOS only works with CDC-ECM
+// - Linux will work on both
+// Note index is Num-1x
+static uint8_t const * const configuration_arr[2] =
+{
+  [CONFIG_NUM_RNDIS-1] = rndis_configuration,
+  [CONFIG_NUM_ECM-1  ] = ecm_configuration
+};
+
 // Invoked when received GET CONFIGURATION DESCRIPTOR
 // Application return pointer to descriptor
 // Descriptor contents must exist long enough for transfer to complete
 uint8_t const * tud_descriptor_configuration_cb(uint8_t index)
 {
-  return (0 == index) ? main_configuration : alt_configuration;
+  return configuration_arr[index];
 }
 
 //--------------------------------------------------------------------+